How to check if a constraint exists

In SQL Server, you can check if a constraint exists using the following script:

SELECT
OBJECT_NAME(OBJECT_ID) AS NameofConstraint
,SCHEMA_NAME(schema_id) AS SchemaName
,OBJECT_NAME(parent_object_id) AS TableName
,type_desc AS ConstraintType
FROM sys.objects
WHERE type_desc LIKE '%CONSTRAINT'
AND OBJECT_NAME(OBJECT_ID)='[constraint name here]'

or by running one of the following commands:

SELECT * FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS where TABLE_Name = '[TableName]'
SELECT *
FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS
WHERE CONSTRAINT_NAME='[constraint name here]'
--Returns one row for each FOREIGN KEY constrain
SELECT *
FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS
WHERE CONSTRAINT_NAME='[constraint name here]'
--Returns one row for each CHECK constraint
SELECT *
FROM INFORMATION_SCHEMA.CHECK_CONSTRAINTS
WHERE CONSTRAINT_NAME='[constraint name here]'